The introduction of herbaceous peony (Paeonia lactiflora Pall.) in low-latitude areas is of great significance to expand the landscape application of this world-famous ornamental. With the hazards of climate warming, warm winters occurs frequently, which makes many excellent northern herbaceous peony cultivars unable to meet their chilling requirements (CR) and leads to their poor growth and flowering in southern China. Exploring the endodormancy release mechanism of underground buds is crucial for improving low-CR cultivar screening and breeding. A systematic study was conducted on P. lactiflora ‘Meiju’, a screened cultivar with a typical low-CR trait introduced from northern China, at the morphological, physiological and molecular levels. The CR value of ‘Meiju’ was further verified as 677.5 CUs based on the UT model and morphological observation. As a kind of signal transducer, reactive oxygen species (ROS) released a signal to enter dormancy, which led to corresponding changes in carbohydrate and hormone metabolism in buds, thus promoting underground buds to acquire strong cold resistance and enter endodormancy. The expression of important genes related to ABA metabolism, such as NCED3, PP2C, CBF4 and ABF2, reached peaks at the critical stage of endodormancy release (9 January) and then decreased rapidly; the expression of the GA2ox8 gene related to GA synthesis increased significantly in the early stage of endodormancy release and decreased rapidly after the release of ecodormancy (23 January). Cytological observation showed that the period when the sugar and starch contents decreased and the ABA/GA ratio decreased was when ‘Meiju’ bud endodormancy was released. This study reveals the endodormancy regulation mechanism of ‘Meiju’ buds with the low-CR trait, which lays a theoretical foundation for breeding new herbaceous peony cultivars with the low-CR trait.

The herbaceous peony (Paeonia lactiflora Pall.) plant is world-renowned for its ornamental, medicinal, edible, and oil values. As global warming intensifies, its growth and development are often affected by high-temperature stress, especially in low-latitude regions. Superoxide dismutase (SOD) is an important enzyme in the plant antioxidant systems and plays vital roles in stress response by maintaining the dynamic balance of reactive oxygen species (ROS) concentrations. To reveal the members of then SOD gene family and their potential roles under high-temperature stress, we performed a comprehensive identification of the SOD gene family in the low-latitude cultivar ‘Hang Baishao’ and analyzed the expression patterns of SOD family genes (PlSODs) in response to high-temperature stress and exogenous hormones. The present study identified ten potential PlSOD genes, encoding 145–261 amino acids, and their molecular weights varied from 15.319 to 29.973 kDa. Phylogenetic analysis indicated that PlSOD genes were categorized into three sub-families, and members within each sub-family exhibited similar conserved motifs. Gene expression analysis suggested that SOD genes were highly expressed in leaves, stems, and dormancy buds. Moreover, RNA-seq data revealed that PlCSD1-1, PlCSD3, and PlFSD1 may be related to high-temperature stress response. Finally, based on the Quantitative Real-time PCR (qRT-PCR) results, seven SOD genes were significantly upregulated in response to high-temperature stress, and exogenous EBR and ABA treatments can enhance high-temperature tolerance in P. lactiflora. Overall, these discoveries lay the foundation for elucidating the function of PlSOD genes for the thermotolerance of herbaceous peony and facilitating the genetic breeding of herbaceous peony cultivars with strong high-temperature resistance.

The growing region of herbaceous peony (Paeonia lactiflora) has been severely constrained due to the intensification of global warming and extreme weather events, especially at low latitudes. Assessing and selecting stress-tolerant and high-quality peony germplasm is essential for maintaining the normal growth and application of peonies under adverse conditions. This study proposed a modified multi-criteria decision-making (MCDM) model for assessing peonies adapted to low-latitude climates based on our previous study. This model is low-cost, timesaving and suitable for screening the adapted peony germplasm under hot and humid climates. The evaluation was conducted through the analytic hierarchy process (AHP), three major criteria, including adaptability-related, ornamental feature-related and growth habits-related criteria, and eighteen sub-criteria were proposed and constructed in this study. The model was validated on fifteen herbaceous peonies cultivars from different latitudes. The results showed that ‘Meiju’, ‘Hang Baishao’, ‘Hongpan Tuojin’ and ‘Bo Baishao’ were assessed as Level I, which have strong growth adaptability and high ornamental values, and were recommended for promotion and application at low latitudes. The reliability and stability of the MCDM model were further confirmed by measuring the chlorophyll fluorescence of the selected adaptive cultivars ‘Meiju’ and ‘Hang Baishao’ and one maladaptive cultivar ‘Zhuguang’. This study could provide a reference for the introduction, breeding and application of perennials under everchanging unfavorable climatic conditions.

Gene function verification is a crucial step in studying the molecular mechanisms regulating various plant life activities. However, a stable and efficient homologous genetic transgenic system for herbaceous peonies has not been established. In this study, using virus-induced gene silencing technology (VIGS), a highly efficient homologous transient verification system with distinctive advantages was proposed, which not only achieves true “intact-plant” infiltration but also minimizes the operation. One-year-old roots of the representative species, Paeonia lactiflora Pall., were used as the materials; prechilling (4 °C) treatment for 3–5 weeks was applied as a critical precondition for P. lactiflora to acquire a certain chilling accumulation. A dormancy-related gene named HOMEOBOX PROTEIN 31 (PlHB31), believed to negatively regulate bud endodormancy release (BER), was chosen as the target gene in this study. GFP fluorescence was detected in directly infiltrated and newly developed roots and buds; the transgenic plantlets exhibited remarkably earlier budbreak, and PlHB31 was significantly downregulated in silenced plantlets. This study established a homologous transient silencing system featuring intact-plant infiltration and minimized manipulation for gene function research, and also offers technical support and serves as a theoretical basis for gene function discovery in numerous other geophytes.

Cold acclimation (CA) is a strategy which plants have evolved to increase freezing tolerance. Global climate change could obstruct CA and raise the probability of winter injury, especially for evergreens. Hence, understanding the regulatory mechanism of CA is crucial to improve freezing tolerance in evergreen plants. A comparative study on a pair of closely related evergreen and deciduous iris species in response to cold through CA was conducive to uncovering and complementing the knowledge of CA. We investigated morphological, physiological and biochemical changes, as well as the expression of associated genes in the functional leaves of both iris species from natural CA to deacclimation. Briefly, fast and strong CA in the evergreen iris might cause early expressions of BAM1, NCED3, GPX6, etc., which leads to strong enzyme activity of starch degradation, abscisic acid biosynthesis and reactive oxygen species scavenging. Additionally, genes belonging to the antioxidant system were mainly induced during deacclimation. These results suggest that interspecies differences in the leaf freezing tolerance of irises are associated with the rate and degree of CA, which activates multiple signaling networks with complex interactions and induces the transcription of cold-responsive genes. Moreover, the ICE–CBF–COR signaling cascade may integrate and initiate diverse cold-responsive pathways during CA of the evergreen iris. The findings of this study provide valuable insight to further research on CA mechanisms and implicate genes which could support breeding strategies in herbaceous perennials under climate changes.